Experiments with some microorganisms which utilize ethane and hydrogen.

An interesting case of extreme specificity of enrichment and selective culture procedures has recently been described for methane-utilizing bacteria (Leadbetter and Foster, 1958). Obligate methane-utilizing pseudomonads (Pseudomonas methanica) invariably were obtained from inocula from a great many natural sources. A further degree of specificity within the group was encountered; it was found that emergence of particular pigmented varieties, to the exclusion of others, can be predicted if the enrichment and isolation procedures follow a set pattern. Almost as surprising was the ineffectuality of those procedures in evoking the appearance of nonexacting methane-utilizing bacteria of the type that can also grow at the expense of other hydrocarbon and nonhydrocarbon substrates (Aiyer, 1920; Bokova et al., 1947; Brown and Strawinski, 1957; Hutton and ZoBell, 1949; KaprAlek, 1954; Muinz, 1915; Nechaeva, 1949; Slavnina, 1948; Tausz and Donath, 1930). This paper documents an additional kind of unusual specificity in connection with gaseous hydrocarbon-utilizing bacteria. Three significant findings reported are (1) the use of natural gas (in which methane is by far the major component) as a substrate in enrichment cultures led to the isolation of many different ethane-utilizing organisms, but none capable of utilizing methane as the sole hydrocarbon for growth; (2) a majority of the ethane-utilizing bacteria proved to be facultative autotrophs capable of developing at the expense of hydrogen gas and carbon dioxide as the respective sole sources of energy and carbon. A preliminary note on this subject has already been published (Dworkin and Foster, 1957); and (3) a